A method of forming metal patterns on a substrate, particularly forming the patterned circuitry on high density electronic packaging, utilizes a technique termed "ablative photodecomposition." This technique involves depositing an organic polymer coating on the substrate to be patterned. The organic coating, which is sensitive to radiation, is then patterned by irradiation from a laser, typically an excimer laser. Commercially available excimer lasers typically emit at either 193 nm, 248 nm, 308 nm or 351 nm. The lasers which emit at 193 nm and 248 nm both require fluorine gas whereas the lasers that emit at 308 nm require a chlorine containing gas. Fluorine gas is more difficult to handle and dispose of than chlorine gas. In ablative photodecomposition, a large number of photons of a particular wavelength are directed to the coating in a short time. The coating, which must be capable of absorbing at the laser wavelength, absorbs a significant portion of these photons and as a result, many polymer chain fragments are produced in a small volume in a very short amount of time. This causes a localized increase in volume which cannot be sustained, and the pressure is relieved by the process of ablation, wherein fragmented chains explode and escape from the coating, leaving an etched material. Thus, fine line patterns can be produced by this technique, without the use of wet, or solvent etching of the coating.
However, with existing ablative photodecomposition methods, one of the disadvantages is that the patterned coating is typically stripped with halogenated solvents; halogenated solvents are the subject of increased environmental regulations. In addition, existing ablative photodecomposition methods typically utilize electroless deposition of metal, typically copper, to fill the ablated pattern. Electroless plating is time and space consuming and requires solvent baths which provide a source for the evaporation of solvents.
It would be desirable to have a convenient method of ablative photodecomposition that utilizes non-halogenated stripping solvents, that does not require electroless plating and that provides high resolution of metal patterns.